This study is being done based on the hypothesis that local control of radiation therapy may be improved by a radiation sensitizer that effectively increases the radiation dose at the tumor, but not in the normal brain. In the lead-in phase, the primary objective is to implement standardized test procedures designed to assess cognitive function and neurologic status, and to confirm safety data in patients receiving Gadolinium Texaphyrin (PCI-0120) Injection (Gd-Tex), 5.0 mg/kg, administered intravenously (IV) two to five hours before each of ten whole brain radiation treatments of 3 Gy. In the randomized phase, to compare whole brain radiation therapy alone (10 fractions of 3 Gy administered over ten treatment days) to whole brain radiation therapy (10 fractions of 3 Gy) plus administration of Gd-Tex at a dose of 5.0 mg/kg IV 2 to 5 hours before each radiation treatment, in terms of: time to death, cause of death, response rate determined by MRI, time to progression of the brain metastases using MRI scans obtained at predetermined intervals, time to deterioration of neuro-cognitive function, quality of life, and acute and chronic toxicity. Another objective of the this trial is to confirm the population pharmacokinetic model developed in Phase II using detailed sampling at three selected study centers and a limited sampling strategy at all other centers. The influence of covariates (LDL cholesterol, HDL cholesterol, total protein, albumin, protein binding, age, weight, gender, renal/hepatic function) on Gd-Tex elimination will be evaluated.